I'm working on a project that will mail out access codes. Yes, using physical snail mail. The recipient needs to be able read the code and accurately type it into a web form. The codes consist of seven characters including upper case A-Z, lower case a-z, and digits 0-9.
My question is how to communicate exact characters, keeping in mind that I might have a number 0 immediately next to the letter O. A code may also contain one, but not the other. I'm also concerned about i vs I vs l vs 1... and those are four different valid characters.
What fonts can I use that will clearly distinguish these? What are tests I can use to check the font? Are there other sets of similar character glyphs I might be missing? Is there anything else that I can/should be doing to make sure these are readable in an accurate way?